It is often necessary to strengthen certain muscles associated with hand movement and a number of devices have been proposed for strengthening of the muscles used to move the fingers and thumb into a clasped position. There is a second group of muscles which are associated with control of the fingers outwardly to a fully extended position.
A number of prior art hand exercisers used in the extension movement of the fingers are disclosed in the following U.S. Pat. Nos.: 3,612,521; 4,679,799; 4,615,522; 3,944,220; and 1,472,9106.
U.S. Pat. No. 3,612,521 uses finger and thumb engaging ports located in an elastic body, but does not have the required cooperation between the ports for the desired finger extension, nor the somewhat independent action of the fingers during extension, such that each finger acts generally independently against the thumb movement.